Heat pump water heater in conjunction with gas water heater

ABSTRACT

A method for heating water delivered and stored in a water heater storage tank includes activating at least one of dual fuel heater types in response to various modes of operation. The water heater is preferably a dual fuel or hybrid heat pump gas water heater that includes a heat pump as the first type of heater for heating the water, and a gas burner as the second type of heater that transfer heat to the water. One or more sensors monitor water temperature and communicate with a controller to activate one of, or both of, the first and second types of heaters. If there is an electrical power outage, the hybrid heat pump gas water heater is still able to heat the water.

BACKGROUND OF THE DISCLOSURE

This disclosure is directed to water heaters, and is more particularlydirected to a hybrid water heater that is also referred to as a dualfuel water heater or hybrid heat pump gas water heater.

One skilled in the art understands that different heat sources offerdifferent advantages, and likewise have different disadvantages. Forexample, full-sized tank water heaters usually require either anelectrical connection in which the circuit is a 220/240 V and 30 ampcircuit or a gas connection capable of supplying 40 to 100 K BTUs perhour. Typically, the tank water heater relies upon a single energysource—either electric or gas. Thus, installations in the home are madebased upon the energy requirements of the water heater. That is, eithera 30 amp connection or a gas connection is provided in order to connectwith an electric or gas water heater, respectively, in the home.

As will be appreciated, replacement water heater units for the home areusually based upon the previous type of installation. For example, ifthe homeowner wants to replace a gas water heater, then a similar sizedgas water heater is purchased to “drop-in” as a replacement. Preferably,the gas and flue connections are substantially identical, the electricalconnection for the gas water heater is similar, and the inlet and outletwater connections are likewise similar to facilitate ease ofreplacement.

On the other hand, rather than merely replacing an electric water heaterwith a new electric water heater, some consumers have opted to switch toa hybrid water heater that uses a highly efficient heat pump waterheater available as a “drop-in” replacement for the electric waterheater market. Typically, the heat pump water heater is operated at 240V and 30 amps so that the replacement hybrid heat pump water heater isdirect wired in the same fashion as a standard electric water heater.Likewise, the same water inlet and outlet configurations are used in thenew heat pump water heater to facilitate replacement. One commerciallyavailable hybrid-type water heater includes multiple resistor typeheaters and a heat pump type heat source used to heat the water in thetank. A controller energizes one or more of these heat sources inresponse to various temperature data inputs. The water temperature andthe rate of temperature change are monitored, and the data input to acontroller which then determines which heat source to use, i.e., thecompressor of the heat pump, the upper electric resistance heater,and/or the lower resistance heater.

Heat pumps are highly efficient but take a longer period of time toraise the temperature of the water in the tank. Gas burners, on theother hand, can quickly raise the temperature of the water in the tank.Nevertheless, no hybrid, heat pump water heater offering is available asa replacement in the gas water heater market. Gas fuel costs versuselectrical costs in some areas make the electrical heat pump waterheaters less attractive in terms of payback. Further, higherinstallation costs are required if a heat pump water heater is installedas a replacement and particularly if the replacement water heaterrequires a 240 volt, 30 amp dedicated circuit. That is, tank gas waterheaters do not require the elevated voltage or amperage in a dedicatedcircuit and therefore a homeowner would have to update the electricalservice if a hybrid heat pump electrical water heater were used toreplace the gas water heater. Likewise, utilities may resist fuelswitching from gas to electric. Hence, a 240 V heat pump water heatermay not be as attractive to a consumer/homeowner or may encounter otherresistance as a replacement to a gas water heater.

Another obstacle to replacing a gas water heater, and particularly onethat is at least partially electric such as a gas heat pump waterheater, is that installation costs are a big factor. Electricalconnections, gas line connections, and the associated flue allcontribute to the potential cost to the homeowner who is considering achange to a gas heat pump water heater as a substitute for the gas waterheater.

Utilities also become a factor. There are times when a utility wants toencourage electrical use, and still other times such as peak demand whenthe utility would prefer that the consumer not use electricity for thewater heater. Therefore, if a homeowner is considering moving away froma gas water heater to electric water heater, for example one that uses240 V, a utility may offer some resistance to such change.

Thus, a need exists for a high-efficiency, hybrid heat pump waterheater, and more specifically a gas heat pump water heater or dual fuelwater heater, replacement to a gas water heater where the heat pumpportion of the hybrid water heater can maintain the hot watertemperature at a lower cost than using a high-powered gas burner whenwater is not being used or when the draw is low. Further, thehigh-efficiency hybrid heat pump water heater is capable of using thevoltage and current level that is readily available in a convenientoutlet located near a gas water heater installation that is beingreplaced. Likewise, the replacement must be as compatible with existingconnections as possible to minimize any cost to the homeowner related tothe changeover, i.e., gas connections, electrical connections, flueconnections, footprint, etc.

SUMMARY OF THE DISCLOSURE

A first exemplary embodiment of the disclosure is directed toward awater heater including a tank body for storing a volume of water. A coldwater supply line delivers water to the tank body. A water dischargeline provides for egress of heated water from the tank body. The waterheater further includes a first type of heater and a second type ofheater using a different energy/fuel source than the first heater typefor heating the water in the tank body.

The disclosure is directed toward a water heater including a tank bodyfor storing a volume of water. The water heater includes a cold watersupply line for delivering water to the tank body and a water dischargeline for egress of heated water from the tank body. The water heaterfurther includes a heat pump for heating the water in the tank body. Thegas burner is mounted within or adjacent but external to the tank bodyto transfer heat to the water stored in the tank body, or the gas burnermay be an instantaneous type water heater that raises the temperature ofthe outlet water.

An exemplary water heating method of the present disclosure includesdelivering water to a tank body through a water supply line and storinga volume of the water in the tank body. The method further includesheating the water in the tank body with a first type of heater, andselectively using a second type of heater using a different energy/fuelsource than the first heater type to heat the water in the tank bodywhen a threshold is met.

One advantage of the present disclosure is to provide a hybrid waterheater that operates with high energy efficiency.

Another advantage of the present disclosure is to provide a water heaterthat reduces costs of operating and installation.

Still another advantage of the present disclosure relates to providing ahigh efficiency electric heat pump to maintain hot water temperature ata lower cost than using a high-powered gas burner when water is notbeing used or when hot water consumption is low or moderate.

Yet another advantage is that with a hybrid gas heat pump water heaterif electrical power is lost, hot water can still be provided to thehomeowner.

The present disclosure provides the consumer a choice of a gas orelectric water heater for new construction, as well as replacing a gaswater heater with a hybrid gas heat pump water heater.

A dual fuel heat pump water heater/gas water heater that can easilydrop-in and replace a standard gas water heater that preferably has thesame inlet and outlet water connections, the same gas vent pipeconnection, same relative footprint, and that will operate in the eventof loss of electrical power.

Still other benefits and advantages of the present disclosure willbecome apparent upon reading and understanding the following detaileddescription

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (FIGS. 1A and 1 b) shows a hybrid heat pump gas water heaterassembly.

FIG. 2 (FIGS. 2A and 2B) is another embodiment of the dual fuel, hybridheat pump gas water heater assembly.

FIG. 3 (FIGS. 3A and 3B) is still another embodiment of the dual fuel,hybrid heat pump gas water heater assembly.

FIG. 4 is a flow-chart for an exemplary mode of operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a multiple heater type water heater (hereinafter“hybrid water heater 10) according to an exemplary embodiment of thedisclosure. The hybrid water heater 10 includes a first heater type 12and a second heater type 14, which is a different fuel or energy sourcefrom the first heater type. More specifically, the first heater type 12is a heat pump system and the second heater type 14 is a gas burnerassembly. It is contemplated that the presently disclosed hybrid waterheater 10 can be installed as an alternative water heater in regions ofthe country that traditionally use a gas water heater, or can be used asa replacement for a gas water heater. When used as a replacement,consideration is also given to ease of replacement and includes drop-infeatures such as aligning and sizing with an exhaust gas flue, gassupply, water connections, and size. For example, the exhaust duct sizemay be 3 inches for 40,000 BTU burners or less, and typically 4 inchdiameter doctors use for burners greater than 40,000 BTUs. Existing gaslines are typically ½ inch and ¾ inch, and the electrical connection ispreferably a 120 V corded plug that can reach a 120V, 15 amp outlet.

The present disclosure is directed toward a stand-alone storage waterheater 10 including a housing 15 that encloses a tank body 16 forstoring a volume of water therein. Cold water is delivered to the tankbody 16 from a water supply line 18 (i.e., a “dip tube”) connected to acold water supply (not shown). This water supply line 18 delivers thecold water toward a bottom portion of the tank body 16, and the deliveryof the cold water displaces a volume of water already contained thereinthe lower region toward a top portion of the tank body. Because warmwater is less dense than cold water, the warmer water rises to the topportion of the tank body 16. Therefore, a water outlet or egress line 20is situated at the top portion of the tank body 16 for delivery ofheated water to various faucets and appliances in the home.

The heat pump 12 is mounted to the tank body 16. One exemplary heat pumpis described in application Ser. No. ______ (Attorney Docket No.60280.0012US01; GE Docket No. 225439) to Nelson, et. al.; however,operation and features of the heat pump are not limited to any onedisclosure. Any known heat pump system may be incorporated into thepresent water heater 10 to achieve a function of the disclosureincluding activation of the heat pump heater type corresponding to atleast one mode of operation. In the illustrated embodiment, the heatpump 12 includes a compressor 24, condenser 28, a restriction, anevaporator 22, and a fan 26. A working fluid circulates through the heatpump to heat the water in the tank body 16. More specifically, the fan26 directs the warm ambient air over the evaporator 22 for transferringheat into the working fluid. The working fluid (e.g., a refrigerant)exits the evaporator 22 in vapor gas form, i.e., in a near gas state.The working fluid is received in the compressor 24, where it increasesin pressure and temperature to an associated superheated gas vapor as itenters the condenser. The vapor enters the condenser 28 and transfersenergy to the water stored in the tank body 16. The working fluid vaporchanges phase to liquid state as the energy is transferred to the water.A throttling device (not shown) receives the working fluid before itreturns to the evaporator.

In the illustrated embodiment, the evaporator 22, the compressor 24, andthe fan 26 are mounted to a top, horizontally extending and planarsurface of the housing 15, however, there is no limitation made hereinto a surface of the housing body of which the various components of theheat pump 12 are supported. In one embodiment, the condenser 28 is incontact with a (e.g., continuous) sidewall surface 30 of the tank body16 for transferring heat to the water contained therein. In thepreferred embodiment, the condenser 28 is in contact with the sidewall30 of greatest surface area, e.g., the elongated sidewall of the tankbody. In the illustrated embodiment, the condenser 28 is preferablywrapped around an exterior sidewall surface of the tank body 16 in ahelical or serpentine fashion, or in any other manner that provides foreffective heat transfer with the tank body. In this embodiment, aninsulator or similar functioning insulating material 29 may surround theouter sidewall surface of the tank body 30 within the housing 15, thuslimiting heat loss to the ambient air. In this manner, the condenser 28is situated between the outer sidewall surface 30 of the tank body 16and the insulator 29. In another contemplated embodiment, the condenser28 can be situated in the interior 32 of the tank body 16 where it is indirect contact with the water. Embodiments are further contemplated inwhich a heat exchanger (not shown) is situated external to the housing15, wherein water is pumped from the tank body at a first temperature,through the heat exchanger where energy is transferred thereto, andreturned to the tank body at a higher temperature.

The second heater type 14 is a gas burner assembly that includes astanding or an intermittent pilot, which ignites a gas flame in a mainburner of the assembly. In the illustrated embodiment of FIG. 1, the gasburner assembly 14 is shown situated at and heating a base portion ofthe tank body 16. The gas burner assembly heats the colder watercontained at the bottom of the tank body 16 due to its greater density.

A majority of the gas water heaters have a 3 inch vent pipe that comesout the top of the appliance, although some have a 4 inch vent pipe.Preferably the drop-in heat pump water heater/gas water heater willreplace a 3 inch vent pipe, although some models could also be availablefor replacing the 4 inch vent pipe. The replacement model for the 3 inchvent pipe will only have a 40,000 BTU maximum burner, whereas a 4 inchvent pipe can accommodate a larger BTU burner. It will also beappreciated that a dual fuel water heater with a 3 inch flue/vent pipecan be installed in a 4 inch vent pipe application. Typically, a ½ inchgas supply line is provided for existing gas water heaters, and thus thedual fuel heat pump water heater of the present disclosure is intendedto serve as a drop-in unit without having to change any of the existinginfrastructure.

In the first configuration of FIGS. 1A and 1B, there is shown a 120 Vheat pump water heater with storage tank and a standard burner. The dualfuel heat pump water heater has the ability to operate with the loss ofelectrical power, it has the ability to drop in and hook up to a 3 inchvent pipe, and uses the same gas supply, that is a ½ inch or ¾ inch gassupply line, as the standard gas water heater that it replaces. Thisdual fuel hybrid heat pump gas water heater does require external powerwhereas an existing gas water heater does not, but the dual fuel hybridheat pump water heater of the present application is designed to connectwith the 120 V circuit (e.g. a cord connection able to plug-in to anearby, convenient electrical outlet versus installation of a dedicated240V, 30 A circuit).

The illustrated embodiment of FIG. 1 shows a flue 34 extendingvertically upwardly coincident or in proximity to a central axis of thehousing 15 or tank body 16. This flue 34 vents byproducts of combustion.The flue gases naturally rise through the flue 34, which extends towardor connects with further ductwork (not shown) terminating at an exteriorof the home. Of course one skilled in the art will appreciate that thepresent disclosure is not limited to a natural draft ventilation systemand that a direct-vent, a horizontally extending vent, or a fan-assistedor power-vented ventilation system can be used without departing fromthe scope and intent of the present disclosure.

Other embodiments are contemplated in which the gas burner assembly issituated proximate to an outer surface of the tank body 16 and spacedfrom a base portion of the tank body 16. One example shown in FIG. 2(FIGS. 2A and 2B) includes a removed gas burner assembly 14 situatedadjacent and exterior to the sidewall 30 of the housing 15. In thisembodiment, it is envisioned that the water can be introduced from thetank body 16 through a conduit 17 that passes in proximity to theignited gas burner assembly 14 in order to heat the water. The waterreturns to the tank body at a temperature higher than the temperature itwas before the gas heater cycle. Since the gas burner assembly 14 issituated at a location removed from directly beneath the bottom surfaceof the tank body 16, a flue extends upwardly from the gas burnerassembly 14 to carry away combustion gases produced therefrom. There areseveral advantages associated with this arrangement: (1) the flue 34does not consume space inside the tank body 16, and hence the tank iscapable of containing a greater volume of water; (2) the flue does notextend outwardly and upwardly from a top surface of the tank body, andtherefore does not obstruct various arrangements for the heat pumpcomponents mounted on the top surface of the water heater; and, (3) theflue does not remove energy from the standing water stored in the tankbody, and therefore does not contribute to lowering the temperature ofthe water surrounding the flue. It does have the disadvantage of anincreased footprint for the water heater (which may not be an issue fornew construction), and possibly impacting ease of replacement of asmaller standard gas water heater.

The heat pump water heater with a gas burner on the side and not on thebottom as shown in FIG. 2 is provided with a 120 V heat pump waterheater, and a storage tank with a side arm style burner that still usesthe same return flow style condenser. The burner heats water in the tankthrough a side arm heat exchanger (i.e. it is not intended as an outletflow instantaneous type water heater design) and thus is intended toraise the tank temperature to a desired temperature level. Generally theburner is much higher capacity than a standard natural draft styleburner (e.g. 40,000 BTU burner) and therefore the same venting cannot beused, and may have to use an increased gas supply (e.g. changing from a½ inch gas supply to a ¾ gas supply line), although it is preferred thatthe gas supply line need not be changed and instead the largest burneravailable without increasing the gas supply line would be desired.

For example, gas line and vent pipe size limitations may govern the“drop-in” envelope requirements of the dual fuel heat pump water heater.It is generally known that a standard gas water heater that is drop-inready has a naturally vented installation, a ½ inch gas line, and a 3 or4 inch vent or vent connector. By definition, a vent exits verticallythrough the roof of a home or similar structure, and exhausts combustionproducts of the naturally-drafted water heater and any othernaturally-drafted appliances. A vent connector attaches from the drafthood of an appliance to the main vent that exits the home. Likewise,appliances may also be attached directly to the vent without a ventconnector. Vent materials may include single or double wall metal pipe,a lined masonry chimney, or other code or agency-approved vent material.For a 3 inch existing vent or vent connector, a drop-in gas water heatermust have a burner rated at 40,000 BTU per hour or below. For a 4 inchexisting vent or vent connector, the burner rating is limited to 134,000BTU per hour (for a 50 foot vent height). Two or more naturally ventedappliances with a 4 inch vent and connectors are limited to 89,000 BTUsper hour for a 100 foot vent height, 86,000 BTUs per hour for a 50 footvent height as provided by the NFPA National Fuel Gas Code vent sizingregulation. The capability of a ½ inch gas line is dependent on thenumber of other gas appliances in the home, the length of the gas linebetween the home meter and the appliance, and the pressure in the gasline. Each consumer or homeowner has a potentially differentinstallation. The maximum ½ inch pipe capacity with a straight length of10 feet will allow for an appliance rated up to 175,000 BTUs per hour(NFPA National Fuel Gas Code vent sizing for pressure less than 2 psi inW.C. Drop). Tankless-style and power-vented gas water heaters can alsobe included, with metal or PVC vents, 2-4 inches in diameter, up to amaximum capacity of a ½ inch gas line as defined above. The drop-in duelfuel heat pump water heater must be able, therefore, to attach to a 3-4inch vent with a maximum burner rating for the 3 inch vent of 40,000BTUs, a 4 inch vent has a maximum 134,000 BTUs, a ½ inch gas line, andpreferably the dual fuel heat pump water heater is able to plug into astandard 120 V outlet so that no dedicated circuit for the water heateris required.

It would also be desirable to not have to change the vent pipe, however,this will be required in some arrangements because code will require aforced draft associated with a tankless burner that requires a fan andcannot be ducted into the same chimney associated with a natural ventingstyle burner. Therefore, some configurations will require venting to anindependent chimney or a wall vent per code requirements.

In still another embodiment of FIG. 3 (FIGS. 3A and 3B), the water canbe routed from the gas burner assembly 14 situated at the outlet (i.e.,outside of the tank body 16 and may be within the housing) and directlyto an appliance or delivery faucet. In the configuration of FIG. 3, theburner 14 is provided on the outlet and is not intended to heat thewater in the entire tank. The heat pump is used to heat the water in thetank, and the burner raises the temperature of the water passing throughthe outlet to the final desired temperature if the tank temperature isnot sufficient to meet the temperature demand. A 120 V heat pump waterheater with the storage tank is provided that uses a high efficiencyburner. The burner of FIG. 3 heats the outlet water, and raises theoutlet temperature to a desired level whenever the heat pump is unableto deliver water at the desired temperature level. The burner capacityof this configuration is limited by the existing gas supply, and in thisarrangement, there is requirement to vent to the independent chimney orthe wall vent per code requirements. Therefore, this configuration ofFIG. 3 (like the embodiment of FIG. 2) has some advantages in replacinga conventional gas water heater, but may not be as desirable as theembodiment of FIG. 1 which more completely matches all of the associatedinfrastructure.

A controller 36 is operatively associated with both the first and thesecond heater types 12 (heat pump), 14 (gas burner). The controller 36selectively energizes the heater types based on data representative ofwater temperature within the interior tank body and/or the occurrence ofa flow event transmitted to the controller 36 for processing. Thecontroller 36 is operatively connected to the first and second heatertypes 12, 14 and includes a module that facilitates the automaticselection and energizing of at least one of the heat pump 12 and the gasassembly 14 in response to the data received that is representative ofthe water temperature and/or flow event.

At least one sensor 38 measures the temperature of the water stored inthe tank body. The controller 36 receives a signal from the sensor(s) 38indicative of the water temperature. The controller 36 can use inputsfrom other sensors to base calculations and to make similardeterminations. The sensor 38, for example, may be situated in or on thetank body 16 to measure water temperature. A first sensor may be placedon or in a lower portion of the tank body 16 to monitor watertemperature in that region. Alternatively, the sensor may be placed inan upper portion of the tank body 16 depending on the particularembodiment of dual fuel, hybrid gas water heater that is used. In stillanother arrangement, at least first and second sensors may be placed onor in at least two regions of the tank body 16.

In other arrangements, additional data or sensor information may beprovided to the controller. For example, a sensor such as a thermistormay be added to monitor one or more of the compressor outlet, theevaporator inlet, evaporator outlet, or sense ambient temperature.However, one skilled in the art will appreciate that these additionalsensors are optional only and may provide greater accuracy or control,although the additional sensors are not required for effective operationof the dual fuel/hybrid heat pump gas water heater.

For example, with respect to the embodiment of FIG. 1, the controllerreceives sensor inputs T1 and T2, i.e. representative of two sensors onthe tank, although it may be possible to use a single sensor to monitorthe tank temperature. If two sensors are used, one of the sensors may beused for the redundant gas control (if power is lost) and the waterheater would be capable of operating without power using the singlesensor. However, if external power is provided, the main controlmonitors the first or upper sensor and operates the water heater basedon this data. In yet another embodiment, two sensors can be used by thesame controller, with the output from the first sensor being used tooperate the first heater type, and the output from the second sensorbeing used to operate the second heater type.

The controller may receive data regarding the evaporator inlet (T3A) andthe evaporator outlet (T3B), the compressor discharge temperature (T4),and ambient temperature (T5). The main control can turn the heat pump onand off as an output, and likewise turn the gas burner on and off as anoutput. In addition, the controller may provide an output signal to anexternal boost fan for ducted kits.

Still further, the main controller may provide for mode selection andthe controller preprogrammed for various modes. For example, in an“economic mode”, heat may only be provided by the heat pump which in thelong run is the most energy efficient. Another choice may be to use a“hybrid” mode in which control could be alternated between the heat pumpand the gas. Still another choice is to use a “standard gas” mode, thatis, to operate the dual fuel heater in a gas only mode. Still anotherchoice may be a “high demand” mode which uses the heat pump and gas as amix, but more readily uses gas. By way of example only, in the “hybrid”mode noted above, gas is used as a backup when the tank is substantiallyemptied but in the “high demand” mode, gas is used readily when the tankis only partially emptied. Still another mode could be “external demandresponse module” in which operation of the dual fuel water heaterdepends on a utility provided real-time signal or data that wouldoperate the water heater as the utility would prefer. In still anothermode, referred to here as a “low dollar cost mode”, the user inputs thegas and electricity rates and the controller then operates the dual fuelwater heater in the lowest cost or expense to the homeowner. Yet anotheroption may be a “peak load control” mode that serves as a balancebetween the homeowners desired use of the dual fuel water heater basedon cost or expense relative to the real-time electric and gas rate datareceived from the utility. Accordingly, the user interface of thecontroller would allow a homeowner to select one of these options ormodes, although one skilled in the art will understand that these modesare representative only and other modes could be used or provided asoptions without departing from the scope and intent of the presentdisclosure.

One feature associated with the present disclosure is an ability toutilize the least expensive utility in regions of the country thatgenerally heat water by only a gas water heater source. It isanticipated that the heat pump 12 portion of the presently disclosedwater heater 10 can operate on a maximum of six amps andone-hundred-twenty volts power, which is a voltage and a current levelreadily available at most convenience outlets located in proximity ofthe water tank installation. Electric utility can be used for the mainheater type source to generally heat the water for slower recoveryperiods, but the gas utility can be used for instances requiring fasterrecovery periods. The threshold value can be programmed into thecontroller 36 to be such that the controller deactivates the firstheater type 12 and actuates the second heater type 14 at values that arethe most economical and cost efficient. The controller may selectivelyset, reset and/or change predetermined temperature thresholds based oninput received from an energy billing device, which indicates periods ofhigh and low energy demand. Alternatively, the temperature thresholdscan be input by a homeowner at a user interface, or the user inputscurrent average gas rates and electrical rates, and the controller usesthe lowest total cost source of the mix/ratio/combination to heat waterat the lowest cost. Other embodiments are contemplated which utilize atwenty Amp, two-hundred-forty volt circuit. Still, there is nolimitation made herein to a capacity or a power range in which the heatpump heater type requires or utilizes.

FIG. 4 illustrates a method of heating water in a water tank utilizingthe two heater types disclosed herein and, more specifically, a methodof heating the water stored in the tank utilizing at least two modes ofoperation. The controller receives inputs at any given time andoperatively manages various modes of operation to achieve settemperatures as shown in FIG. 4. The method starts at step 200. The tankbody is filled with water from an external water supply source throughthe water supply line at step 202. This water is generally cold and/orcooler in temperature than the water stored in the tank depending on theseason and the source of supply. The controller receives a signal 204from a water tank sensor indicative of the temperature of the water. Thetemperature is compared against a threshold temperature value 206. Thecontroller actuates the first heater type 208 if the water temperatureis below the temperature threshold value. The controller morespecifically actuates the first heater type 208 by controlling the powersupply to the heat pump fan(s) and power to the compressor.

Another instance when water may fall below the temperature thresholdvalue is when the water volume is left in the tank for long durations.For example, if there is no water displacement occurring as a result ofwater removed from the tank for delivery to faucets and appliances, thenthe tank water may fall below the desired temperature threshold value.In both instances, the controller can actuate the first heater type 208to heat the water to the desired temperature. For example, thecontroller actuates the first heater type 208 to heat the water to atemperature having a preselected threshold value. In another embodiment,the controller 36 may also set and adjust threshold temperature valuesbased on predicted demands, which the controller estimates usingprevious water usage patterns that it tracks. The user interface (notshown) may also be included on an exterior of the water tank 10 foruser-input, wherein user-selected temperature threshold settings may beprogrammed into the controller for the predetermined values used in thecontroller calculations.

The first heater type preferably maintains the value above the set-point210. In one embodiment, the controller de-energizes 212 the first heatertype once the temperature of the water reaches above the set-pointtemperature. The first heater type then re-energizes 212 when thetemperature falls below the set point.

Dual fuel water heaters are also dependent on the relative costs of thedifferent fuels. At times, electricity may be a more stable cost andthereby a utility may encourage the homeowner to use the heat pump andonly occasionally use the backup or gas burner during those periods ofpeak need. Thus, interaction or communication with utility is oftenrequired so that the homeowner is encouraged to flexibly use the dualfuel water heater and take advantage of benefits offered by the utility,for example in terms of cost. If the homeowner has only a single fuelwater heater, the choice in response to communication from the utilitywould be a simple on/off condition, i.e., either use the water heater ordon't use the water heater dependent on the communication received fromthe utility. However, with the dual fuel water heater, the choices forthe homeowner are much wider ranging. Therefore, the homeowner mayselect one fuel or another based simply on cost, while the utility mayencourage one fuel or another based on what is best for the overall gridor utility system. It will be appreciated that the homeowner choice, andthat being encouraged by the utility company, may not always be thesame. However, if the water heater is capable of catering to either theselection of the homeowner or the suggestion proffered by the utility,then the options or solutions can likely be satisfied with a dual fuelwater heater. Generally, however, the homeowner will be encouraged touse the heat pump to slowly and more efficiently heat the water storedin the tank. Further, and as noted above, the dual fuel water heateroffers the advantage of providing heated water even when electricalpower is lost. Likewise, providing a drop-in replacement that is highlyefficient is also achieved.

The disclosure has been described with reference to the preferredembodiments. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the disclosure be construed asincluding all such modifications and alterations.

1. A water heater, comprising: a tank body for storing a volume ofassociated water, including: a cold water supply line for deliveringassociated water to the tank body, and, a water discharge line foregress of heated associated water from the tank body; a first type ofheater for heating the associated water in the tank body; and, a secondtype of heater having a different energy/fuel source than the firstheater type for heating the associated water.
 2. The water heater ofclaim 1, wherein the first heater type includes a heat pump.
 3. Thewater heater of claim 2, wherein the heat pump includes: an evaporator;a compressor operatively associated with the evaporator; a condenser fortransferring heat thereto; a restriction, and a fan operativelyassociated with the evaporator for directing ambient air over theevaporator and transferring heat thereto.
 4. The water heater of claim3, wherein the condenser is wrapped around an outer surface of the tankbody.
 5. The water heater of claim 1, wherein the second heater type isa gas burner.
 6. The water heater of claim 5, wherein the gas burnerassembly is situated at and heats a base portion of the tank body. 7.The water heater of claim 5, wherein the gas burner assembly is situatedproximate to the tank body.
 8. The water heater of claim 1, furtherincluding: at least one sensor for measuring a temperature of theassociated water stored in the tank body; and, a controller receiving asignal from the at least one sensor indicative of associated watertemperature; and, the controller actuates at least one of the first andsecond heaters in response to the sensed temperature.
 9. The waterheater of claim 1 wherein one of the first and second heater types isoperational in the event of an electrical power outage.
 10. A method ofheating water, comprising: delivering water to a tank body through awater supply line; storing a volume of the water in the tank body;heating the water in the tank body with a first type of heater; and,selectively using a second type of heater having a different energy/fuelsource than the first heater type to heat the water when a threshold ismet.
 11. The method of claim 10, further including using a heat pumpassembly for the first heater type.
 12. The method of claim 11, furtherincluding using a gas burner assembly for the second heater type. 13.The method of claim 10, wherein a first heater type heats the water to apreselect temperature, and a second heater type supplements heating ofthe water.
 14. The method of claim 10, wherein the first heater type isa heat pump and the second heater type is a gas burner assembly.
 15. Awater heater, comprising: a tank body for storing a volume of associatedwater, including: a cold water supply line for delivering associatedwater to the tank body, and, a water discharge line for egress of heatedassociated water from the tank body; a heat pump for heating theassociated water in the tank body with an associated working fluid thatcirculates through the heat pump, including: an evaporator, acompressor, a condenser for transferring heat to the associated waterstored in the tank body, a throttling device, and, a fan for directingair over the evaporator and transferring heat from the air to theassociated working fluid in the evaporator; and, a gas burner assemblyfor heating the associated water; at least one sensor for measuring atemperature of associated water stored in the tank body; and, acontroller receiving a signal indicative of the temperature of theassociated water and selectively using the heat pump and/or gas burner.16. The water heater of claim 15, wherein the controller actuates thegas burner assembly if a relative temperature change over a preselecttime period exceeds a threshold value.
 17. The water heater of claim 15,wherein the condenser is received around an outer surface of the tankbody.
 18. The water heater of claim 15, wherein the gas burner assemblyis situated at and heats a base portion of the tank body.
 19. The waterheater of claim 15, wherein the gas burner assembly is situatedproximate to a surface of the tank body.
 20. The water heater of claim15 further comprising a demand response module for communicating with anassociated utility, and a controller that receives data input from thewater heater and the utility to determine a desired operation of thewater heater.
 21. The water heater of claim 15 wherein the condenser iseither located remotely and water from the tank body is recirculated viaa pump or via natural convection to the condenser and back to the tankbody, or the condenser is in direct contact with water in the tank body.